Because divorce is nonexistent in the Philippines, if you enter into a relationship with a married woman while in the Philippines, and she is not legally separated, then you are committing adultery.
The law relating to adultery is this:

The Revised Penal Code defines “adultery” in
Article 333 as follows: “Adultery is committed
by any married woman who shall have sexual
intercourse with a man not her husband and by
the man who has carnal knowledge of her
knowing her to be married, even if the marriage
be subsequently declared void. Adultery shall
be punished by prison correctional in its medium
and maximum periods
(I think those minimum and maximum periods are from 7 to 14 years)

Cohabitation of a foreigner with an unmarried filipina is classified as concubinage, which is also a crime. So living with an unmarried woman is also a crime in the Philippines.
The law relating to concubinage is this:

Art. 334. Concubinage. — Any husband who shall keep
a mistress in the conjugal dwelling, or shall have sexual intercourse,
under scandalous circumstances, with a woman who is not his wife,
or shall cohabit with her in any other place, shall be punished by
prison correctional in its minimum and medium periods.
The concubine shall suffer the penalty of destierro.

The penalty for concubinage is lower than that of adultery. The penalty for the concubine is only destierro, while the penalty for the man for adultery is the same as that of the guilty wife. Destierro means banishment or only a prohibition from residing within the radius of 25 kilometers from the actual residence of the accused for a specified length of time. It is not imprisonment.